The consumer faces a profound number of possible choices when selecting most kinds of products, be it movies, music, books, travel, art, dining, employers, and so on, to the extent that the consumer must choose from well-publicized possibilities, such as through advertising, or rely on recommendations of others. In the first case the set of choices is severely limited to those that can be promoted to a broad audience. In the second case the consumer must weigh the similarity of his or her own tastes to the person making the recommendation, whether it be an acquaintance or media. In addition, the number of possibilities and the cost of acquisition, both in terms of time and money, of assessing possibilities, make it infeasible to sample a large number of possibilities to determine which are of interest to the consumer.
Recommendation systems rely on trying to best match a person's individual preferences to the characteristics of the available items. In general what is known about the subjects and objects is the set of affinities between subjects and objects, where the affinity {Aij} between subject i and object j is determined by explicit feedback from the subject or inferred from the subject's interaction (or non-interaction) with the object. The consistency of the affinity scale from subject to subject and object to object derives from the consistency of the goal of the subjects in the given environment, for example to make a purchase in a commerce environment or to read articles in a content environment.
The primary goal of the recommendation system is to predict for a given subject those objects for which the subject will have the greatest affinity. In general the subject characteristics can be represented by a vector S=(S1, S2, . . . , SL) and the object characteristics can be represented by a vector B=(B1, B2, . . . , BM), whereby the predicted affinity of the subject to the object is a function P=f(S, B). Various recommendation systems then differ in their representation of subject and object characteristics S and B and the similarity function f.
One method that has been used, commonly referred to as collaborative filtering, is to represent the subject as the set of object ratings that the subject has provided; i.e., S={R1, R2, . . . , RL}, where Ri is the subject's rating of object i. In most scenarios where recommendations are of use, the number of available items (e.g., such as catalog size) is going to be much larger than the number of items that have been rated by the subject, and so the set S is sparse. To generate a recommendation of a particular object to a particular subject, the subject's profile is compared to the profiles of other subjects that have rated the object. Given the similarities and dissimilarities of objects that have been rated in common, an estimate of the subject's response is generated. In a recommendation system, the system would generate estimates for a variety of objects rated by similar people and return as recommendations the objects with the highest predicted ratings.
Effectively, this type of system is a “mentored” system, whereby each subject is matched to a set of other subjects with similar tastes that have rated objects that the subject has not rated. This approach has several drawbacks, which include: recommendations can only be made where the subject's small set of mentors have provided coverage; the method is dependent on a class of users that have provided a large number of ratings (i.e., mentors), or else the system database must be searched to provide mentors appropriate to each requested object; the method is limited in capacity to make recommendations across various categories (cross marketing); the method does not make full use of all data for each subject (that is, the method is restricted to the subset of mentors); the representation of the subject, which is the set of ratings for each rated object, is not compact and increases linearly with the number of rated objects; subject representations are not portable to other recommendation systems; requires lengthy questionnaires to introduce a new subject into the system; and faces combinatorial challenges to find the best mentor for a given user and is therefore not scalable to large user populations.
Additional desired characteristics of a recommendation system that cannot be addressed by the mentor method include inverse modeling of subject representations back to physical attributes, such as demographics or psychographics, and identification and representation of object similarities.
Another approach is shopping basket analysis, which makes suggestions based on objects that have been purchased by other subjects at the same time as an object that has been selected by the targeted subject. However, this approach relies on transactional dependency and does not allow prediction of preference for objects that are not purchased together. In particular this method cannot associate subject/object affinities across catalog or across time as catalog items are replaced by similar items. Shopping basket analysis is also not specific to individual subjects, but rather to aggregate transaction histories across all subjects. By contrast, the present invention automatically normalizes all product profiles across product categories and can combine information across single vendor transaction histories.
Other approaches classify objects according to expert defined categories or attributes, whereby each object is rated by each attribute and then recommendations are made by matching the expressed interests of the subject to the attributes of the objects. Expert systems have the drawback that they are not self-adapting; that is, they require expert classification or coding. This means that such systems are specific to a single product domain. Also, because they are not data driven, they are not able to process large, diverse, and constantly changing transaction histories.
Predictive modeling techniques use demographics to model subjects. Not only are demographics an indirect substitute for aesthetic opinions and therefore inherently inaccurate, this is invasive of the subject's privacy and only specific to groups of subjects and not to individual subjects.